The present invention relates to a device for sampling a plurality of parts of a light beam, in particular a laser beam.
This device includes at least one optical component which is designed to produce two optical samples from a light beam with parallel rays, with no ghost images.
The invention applies in particular to diagnostics on laser beams.
In this field it is often necessary to have several separate samples of a beam in order to achieve complete characterisation of it.
From now on we hereby indicate that the above mentioned component allows the generation of three distinct, completely decoupled and ghost-free diagnostic paths. Photometric measurement of the paths may be managed in a conventional manner by the type of semi-reflecting treatment deposited on each face of the component.
In order to sample one or more parts of a light beam, in particular a laser beam, the use of a plate 2 (FIG. 1) is known which has two flat parallel faces, or a prismatic plate 4 (FIG. 2), or a beam-splitter cube 6 (FIG. 3), or a diffractive component 8 (FIG. 4).
The components shown in FIGS. 1 to 3 only produce a single sampling path 10 from an incident light beam 12, and the diffractive component 8 produces as many samples 14 as there are orders of diffraction.
Furthermore, in addition to the sample 10, the plate with flat parallel faces 2 generally produces several ghost beams. One of the latter 15 is seen in FIG. 1. It is parallel to the beam 16 transmitted by the cube 2 and two other ghost beams 18 can be seen which are parallel to the ghost beam 10 reflected by this cube.
The amplitude of the most significant of the ghost beams is typically 10% of the incident beam 12, and this could prove problematic with a coherent beam because of the interferences which result from it.
The prismatic plate 4 partly resolves this problem: In FIG. 2 it can be seen that the ghost beams 20 and 22 have directions which are respectively separate from that of the reflected beam 10 and that of the transmitted bream 24, but the separation is poor and the transmitted beam 24 is deviated, which complicates the mechanical incorporation of the analysis system (not shown) which uses the prismatic plate.
The beam-splitter cube 6 resolves the problem of ghost imaging well enough. Indeed, there can be seen in FIG. 3 two ghost beams 26 and 28 which are respectively parallel to the reflected beam 10 and to the transmitted beam 30, and the maximum ghost amplitude is typically a hundred times less than that of the incident beam 12. The cube 6, however, only produces one sample.
As for the diffractive component 8, this generates several samples 14 and fully resolves the problem of ghost imaging. It does, however, result in temporal distortion of a pulsed light beam and produces dispersion of a beam which is not perfectly single-mode. Two diffractive components must then be used to partly resolve these distortion and dispersion problems.